Originally Posted by stock49
Yes exactly. When the engine is installed the crank is riding on the shells in the bearing caps and a film of oil - with the upper bearing shells providing the clearance were the oil pressure is delivered. The distance above the parting lines is an engineering spec - with upper and lower bearing shells being matched.

I checked the '54 in my garage - its front bearing cap looks identical yours but it does have a casting number (3701245) along with that same raised dot casting mark between the oil drain holes:

So this older design cap may well be of use to you (with the newer design bearing shells). But there are some details to look after when you are measuring the clearances.

The 1954 and First Series 1955 engines still used shims to establish a precise fit on a particular block and crank pairing:
[Linked Image]
This meant that during assembly all four caps were measured and selectively fit with shims of differing thickness'.

The second series 1955-62 engines used more precisely ground caps and bearings which allowed an engine to simply be assembled without shims:

As you can see the specifications on the cranks and bearings are pretty much identical (GM engineers also gave up the fractions in favor decimals). The newer design calls for tighter clearances on the front two caps vs the rear two.

If it were in my garage I would proceed as follows. Take the old (broken) cap and the old bearing shell and measure the clearance with Plastigauge - crush-able plastic that is placed between bearing and bearing surface: torqued to spec and then remove the cap and bearing shell and read the clearance. Clean off the crushed plastic and replace it with new. Now repeat the process using the old bearing shell and the new Cap. I am curious to see if the clearances are different and if so by how much.

But before you do anything - I have an important question. Are you trying to avoid taking the crank out of the block?

First, thank you for the information and advice. It is exactly what another friend suggested I do this morning when we spoke. Second, no I'm not necessarily trying to avoid taking the crank out, although if I don't need to that it would be a bonus.

When I bought this truck, I received a box full of photos and receipts for everything that was spent on this truck in the past ten years before it went dormant. The engine was rebuilt with new valve seats, push rods, lifters, and even new pistons and the block was bored out slightly, etc. While the engine has sat for a considerable amount of time, it appears to be in very good condition.

That being said, I'm trying to use this unexpected setback to clean up as much as I can without pouring thousands more into the project. Replacing all the gaskets and seals is a good step, I had the transmission rebuilt and I've purchased a new pressure plate and clutch disk. I've pounded most of the dents out of the oil pan and pulled the head, cleaning up everywhere that needs cleaning up. If my engine builder buddy thinks I really should pull the crank and do a line bore, then I guess I'll go along with it. But this platigauge step seems to be a good opportunity to see what the next step should be.

"I don't have a carbon footprint, I drive everywhere."